The invention relates to a device for sealing tray-shaped or pot-shaped receptacles, such as for example blister packs or pots for storing dairy products such as yoghurt, curd cheese or coffee cream. Said device is provided with a sealing head comprising a sealing contour support and a heatable sealing contour and a support plate with at least one guide bolt immobilized thereon which allows for a linear displacement of the sealing head relative to the support plate. At least one spring element impinges the sealing head with a force pointing away from the support plate. A spring seat plate is disposed between the sealing and the support plate and can be linearly displaced in the same direction as the sealing head. A rubber mount associated with the sealing head serves as a joint element and allows the sealing contour support to be tilted about the axis that are perpendicular to the aforementioned guide bolts. An adjusting element is interposed between the spring seat plate and the sealing head.
Blister packs are used for packaging of small components such as for example tablets, pills or buttons, but also sensitive or comparatively expensive components like lenses or electronic components. The mentioned packs consist of a more solid plastic dish with convexities where the remaining parts are kept and a foil cover which seals the convexities hermetically. In most cases the foil cover is glued onto the dish and has an adhesive film correspondingly which as a rule can be activated thermally. The strength of the bonding and/or of the foil cover is adjusted in such a way that on the one hand it adheres to the dish adequately and on the other hand can also be pulled off the dish.
In the same way pasty food which has comparatively small portions can be stored in receptacles which are closed with a foil cover which is easily removable. For example such packaging is used for yoghurt, curd cheese, coffee cream or ready-to-serve pudding.
For applying the foil cover sealing devices will be used which as a rule have several heatable sealing contours. The sealing contour has the task to press the foil cover with a defined force along the outline onto the dish or the cup rim and as a result of the adjusted higher temperature to glue the foil cover together with the receptacle. Sealing in the sense of this invention at issue means processes in which openings of receptacles will be closed with foils. In colloquial terms the notion bonding or welding is used.
In the actual technical state there exists a device for sealing blister packs, which consists essentially of a support plate and several sealing heads. There are bore holes in the support plate in which are guide bolts which are jointed firmly with a sealing head. This construction in hand allows a linear displacement of the sealing head relative to the support plate whereby between sealing head and support plate arranged springs which are enclosing bolts impinges the sealing heads with a force pointing away from the support plate.
Each sealing head has at its face pointing away from the support plate a heatable sealing contour plate. This construction in hand due to the actual technical state the heating is a semiconductor resistor heating and firmly integrated into the sealing contour plate. The setting of the sealing contour plate on the sealing head takes place with a cardan joint which is carrying out here as a ball which is arranged between two plate-formed elements of the sealing head. The ball makes tilting of the sealing contour plate with small angles possible, but also twisting the sealing contour plate about an axis which is perpendicular to the contour.
Sealing heads and support plate forming a unit which is for implementing the sealing attached on the foil cover of the blister pack. In this process each sealing head will come after attaching of the sealing contour into a rest position while the support plate will be shifted relatively to the sealing head and so far until the spring elements which are arranged between support plate and sealing heads produce the desired contact pressure of the sealing contours on the foil cover.
This construction due to the actual technical state have several disadvantages which lead to malfunctioning and production stop of the packaging machine.
Experience shows that an essential reason for malfunctioning lies in the construction of the heating. Particularly a problem is the contact of the resistor element which does not withstand the permanent temperature. Moreover the withstanding of the semiconductors turn out to be insufficiently small. The disadvantage consequence is that the heating often breaks down and therefore has to be changed. Due to the fact that sealing contour and heating are forming a unit, which moreover cannot be removed when built-in with the sealing head, for changing the heatable sealing contour there has to be a complete removal of the unit consisting of sealing heads and support plate. The disassembly requires much effort which costs money and there are also production stops of the packaging machine which cause high loss of production.
The unsatisfactory mechanical stability of the device due to the actual technical state has proven as a disadvantage. The setting of the sealing contour plate on the sealing head with the help of a ball joint makes the location of the sealing contour parallel to the foil cover possible. On the other hand it allows a twisting of the sealing contour plate about an axis which is perpendicular to the contour. This last mentioned possibility of motion has a special disadvantage because it hinders an exact location of the sealing contour relatively to the convexity of the lower plastic receptacle.
On the mentioned device can occur also problems with the exact set-up of the contact pressure of the sealing contour onto the foil cover. Herewith the spring path of the corresponding spring element must be adjusted with the help of screws which operate in axial direction of the spring. Due to the fact that these screws are not easily accessible the setting-up needs a considerable amount of effort and cannot be done during operation which is of great disadvantage.
The linear guiding of the sealing heads by guiding bolts whose ends are attached to a sealing head, each one individually. The other end of the guiding bolts which functions in a borehole of the support plate has not proven as a success. In this carrying out the unity out of sealing head and guiding bolt has a long lever arm which leads from the sealing contour to the guiding borehole in the support plate. Slight loose between borehole and guiding bolts causes the effect that the sealing contour can make considerable lateral motions. These motions also hinder an exact location of the sealing contour relatively to the convexity of the lower plastic receptacle.